Volatile allosteric antagonists of mosquito odorant receptors inhibit normal odor-dependent behaviors

Abstract

Odorant-dependent behaviors in insects are triggered by the binding of odorant ligands to the variable subunits of heteromeric olfactory receptors. Previous studies have shown, however, that specific odor binding to ORco, the common subunit of odorant receptor heteromers, may alter allosterically olfactory receptor function and affect profoundly subsequent behavioral responses. Here we report on the identification of several antagonists of the odorant receptor co-receptor of the African malaria vector Anopheles gambiae, AgamORco, in a small collection of natural volatile organic compounds (VOCs) using a relevant insect cell-based screening platform. Because some of the identified antagonists were previously shown to strongly repel Anopheles and Culex mosquitoes, here we examined the bioactivities of the identified antagonists against Aedes, the third major genus of the Culicidae family. The tested antagonists were found to inhibit the function of Ae. aegypti ORco ex vivo and repel Asian tiger, Ae. albopictus, adult mosquitoes. Specific antagonist binary mixtures elicited higher repellency than single antagonists. Binding competition assays suggested antagonist binding to distinct ORco sites as a likely cause for the enhanced repellence of the blends. These findings demonstrate that a simple screening assay may be used for the identification of allosteric modifiers of olfactory-driven behaviors capable of providing enhanced indoor and outdoor protection against multiple mosquito borne infectious diseases.